The present invention relates to hammer devices for printers.
Serial printers equipped with a series of character types are now in wide use for printing ordinary letters in offices as well as for printing computer and telex output data. Today, there is a keen demand for a printer which is operable at a high speed to reproduce data of a good quality, in connection with the development of word processors in particular.
A quality printer may be one which prints out characters at exact predetermined pitches and with an even density both in each character and throughout characters. To print characters accurately at predetermined pitches, a carriage must be precisely positioned in the transverse direction at each printing position and, for this purpose, a servo motor system is utilized which is capable of accurate positioning control. The positioning accuracy also depends on the accuracy of division or circumferential spacings between adjacent ones of multiple fingers which are arranged radially on a type wheel. However, considering production on industrial basis, type wheels cannot avoid some errors in the accuracy of division or some deformation of their fingers.
With the above in view, a hammering structure with detent means is employed particularly for a daisy type wheel in which the accuracy of division is of prime importance. Specifically, a fount detent in the form of a projection (or a recess) is positioned on the back of each type on a type wheel in alignment with the center axis of the type. A hammer assembly on the other hand has at its front end a detent portion in the form of a recess (or a projection) complementary in shape to the fount detent. When the detent on the hammer assembly is driven into mating contact with a selected fount detent on the type wheel, a corresponding character is printed with the type wheel located accurately in its printing position. The hammer assembly has to perform translation toward the type wheel, involve a minimum of lateral oscillation and be excellent in its durability and ability to follow high-speed operations. None of hammer structures heretofore proposed or put to practical use have been successful in fully meeting such requirements.
Another known type of hammer assembly employs a hammer having a fulcrum of rotation. This type of hammer assembly, however, encounters difficulty in aligning the direction of hammer to fount contact direction with the printing direction of a fount during a printing action. Though the printing position may be accurately regulated, a character becomes uneven in the density distribution due to local contact of the hammer with a fount resulting in poor quality data recording.